misc: Eliminate use of assert!((...).is_ok())

Asserting on .is_ok()/.is_err() leads to hard to debug failures (as if
the test fails, it will only say "assertion failed: false". We replace
these with `.unwrap()`, which also prints the exact error variant that
was unexpectedly encountered (we can to this these days thanks to
efforts to implement Display and Debug for our error types). If the
assert!((...).is_ok()) was followed by an .unwrap() anyway, we just drop
the assert.

Inspired by and quoted from @roypat.

Signed-off-by: Ruoqing He <heruoqing@iscas.ac.cn>

devices/src/legacy/serial.rs

@@ -434,7 +434,7 @@ mod tests {
 
         // write 1 to the interrupt event fd, so that read doesn't block in case the event fd
         // counter doesn't change (for 0 it blocks)
-        assert!(intr_evt.write(1).is_ok());
+        intr_evt.write(1).unwrap();
         serial.write(0, IER as u64, &[IER_RECV_BIT]);
         serial.queue_input_bytes(b"abc").unwrap();
 
@@ -471,7 +471,7 @@ mod tests {
 
         // write 1 to the interrupt event fd, so that read doesn't block in case the event fd
         // counter doesn't change (for 0 it blocks)
-        assert!(intr_evt.write(1).is_ok());
+        intr_evt.write(1).unwrap();
         serial.write(0, IER as u64, &[IER_THR_BIT]);
         serial.write(0, DATA as u64, b"a");
 

devices/src/legacy/uart_pl011.rs

@@ -549,7 +549,7 @@ mod tests {
 
         // write 1 to the interrupt event fd, so that read doesn't block in case the event fd
         // counter doesn't change (for 0 it blocks)
-        assert!(intr_evt.write(1).is_ok());
+        intr_evt.write(1).unwrap();
         pl011.queue_input_bytes(b"abc").unwrap();
 
         assert_eq!(intr_evt.read().unwrap(), 2);